The purpose of the study is to define in physiologic terms the limits of pulmonary function in the small premature. Application of this knowledge to the clinical problem of respiratory insufficiency will suggest new therapeutic maneuvers anticipated to improve mortality and reduce physical amd mental morbidity in this high risk group. The project will identify specific abnormalities in lung function, as preliminary observations suggest that they are extensive. Studies will be carried out to attempt to improve pulmonary function by increasing lung volume.